Musharraf, a key ally in the US-led war on terrorism, escaped an attempt to kill him on 14 December 2003 when a bomb blew up a bridge in the garrison city of Rawalpindi, adjoining the capital Islamabad, minutes after his motorcade passed it.

Musharraf escaped unharmed because a hi-tech jamming device on his Mercedes delayed the detonation of five bombs.

"Four men have been handed down the death sentence in the bridge blast case today," an intelligence official said on Tuesday.

He said two other men were given life sentences. He declined to identify them or give more details.

Some sources say the 14 December attack involved more than a dozen air force technicians from the main Chaklala airbase outside Islamabad, supported by a few junior army officials and a civilian.

In August, Pakistani authorities hanged a man convicted in the same assassination attempt.

Second attempt

On 25 December 2003, Musharraf survived a second bid on his life when attackers rammed a car bomb into his motorcade, killing 15 people.

Five Muslim activists, including a soldier, were sentenced to death in August for the second attempt.

A soldier stands guard at the site
of the 14 December blast

Pakistan's military says no senior officers were involved, and the principal planners were Abu Faraj Farj al Liby, the so-called al-Qaida Number Three arrested in May and handed over to the US, and Amjad Farooqi, a Pakistani extremist gunned down last year.

Musharraf was allegedly targeted by al-Qaida after he pledged support for the US-led war on terrorism in the wake of 11 September 2001, attacks on the US and for withdrawing support for the Taliban harbouring Osama bin Ladin's network in neighbouring Afghanistan.

Home-grown groups, some with ties to al-Qaida, have carried out a series of attacks over the past four years to vent their anger over Musharraf's policies.

In May, Pakistan arrested an air force official who escaped jail late last year after being sentenced to death for the bridge bombing.